A power amplifier is an indispensable component in a communications system. The power amplifier itself is a nonlinear system. An efficiency and a linearity of the power amplifier are inversely proportional; that is, higher efficiency of the power amplifier indicates its lower linearity or higher nonlinearity. From the perspective of energy conversion, the system requires a high-efficiency power amplifier, and at this time the nonlinearity of the power amplifier is extremely high. This causes nonlinear distortion of the power amplifier. The nonlinear distortion of the power amplifier will cause an ACLR (Adjacent Channel Leakage Ratio) of a transmitted signal to exceed the range specified in a 3GPP (The 3rd Generation Partnership Project) protocol. Serious nonlinear distortion may even cause in-band signal distortion, and finally cause an increased error code rate in the system. This requires that digital predistortion processing be performed for signals with nonlinear distortion caused by the power amplifier, so that the ACLR of a signal output by the power amplifier meets the requirement in the 3GPP protocol.
In an existing digital predistortion implementation solution, an independent dedicated chain for collecting data output by the power amplifier is required, where the chain includes a BPF (Band Pass Filter), an LO (Local Oscillator), an LPF (Low Pass Filter), and the like. Meanwhile, the dedicated chain for collecting data output by the power amplifier cannot introduce new nonlinear distortion. Otherwise, a predistortion factor calculated by an adaptive factor updating module will include the nonlinearity of the dedicated chain for collecting data output by the power amplifier, which causes that a predistorter cannot properly compensate for the nonlinearity of a transmit chain. This poses a higher requirement for the dedicated chain for collecting data output by the power amplifier, and a series of functions, such as eliminating a residual frequency deviation and correcting a sampling deviation, needs to be added. This finally causes complex and costly circuits in implementation of the dedicated chain for collecting data output by the power amplifier.